Now that CPUs, driver ICs, memories and other electronic chips used in electronic equipment have made great progress toward higher performance, higher operating speed, size reduction and higher integration, they generate large amounts of heat by themselves. A temperature ramp of a chip by such heat causes malfunction and even failure to the chip. Thus, a number of heat dissipating techniques and heat dissipating members used therefore have been proposed for restraining the chip from a temperature rise during operation.
In prior art electronic equipment or the like, heat-dissipating members using metal plates having a high heat conductivity such as aluminum or copper, often referred to as heat sinks, are used in combination with heat-generating members for restraining any temperature rise in the heat-generating members during operation. One approach for facilitating the transfer of the heat produced within the heat-generating member to the heat-dissipating member is to interpose a flexible sheet between the heat-generating member and the heat-dissipating member. This sheet ensures efficient heat transfer from the heat-generating member to the heat-dissipating member.
In this regard, an increased degree of contact between the sheet and the heat-generating and dissipating members reduces the contact thermal resistance and increases the efficiency of heat dissipation. In the event the sheet has a high hardness, a higher stress must be applied to the sheet and the heat-generating and dissipating members in order to bring them in closer contact for reducing the contact thermal resistance, but can have detrimental impact on both the members.
If the sheet has a low hardness, then the degree of contact between the sheet and the heat-generating and dissipating members can be increased without applying a substantial stress. However, the low hardness sheet is known to have the drawbacks that the sheet can be stretched during handling and the sheet is awkward to handle due to increased tack on the surface.
To solve these problems, a combination technique was employed such as by laying a low hardness sheet on a high hardness sheet. This technique enables to manufacture a composite sheet which is easy to handle and provides a high degree of contact under low stress conditions. This technique, however, requires complex and time-consuming steps for the manufacture, leading to the drawbacks of reduced yields and increased costs.
For the related technology, reference should be made to JP-A 2002-33427 and JP-A 2002-261206.